This invention relates to reverse cementing operations. In particular, this invention relates to methods and apparatuses for floating the casing and controlling fluid flow through the casing shoe.
After a well for the production of oil and/or gas has been drilled, casing may be run into the wellbore and cemented. In conventional cementing operations, a cement composition is displaced down the inner diameter of the casing. The cement composition is displaced downward into the casing until it exits the bottom of the casing into the annular space between the outer diameter of the casing and the wellbore apparatus. It is then pumped up the annulus until a desired portion of the annulus if filled.
The casing may also be cemented into a wellbore by utilizing what is known as a reverse-cementing method. The reverse-cementing method comprises displacing a cement composition into the annulus at the surface. As the cement composition is pumped down the annulus, well fluids ahead of the cement composition are displaced down and around the lower end of the casing string and up the inner diameter of the casing string and out to surface. The fluids ahead of the cement composition may also be displaced upwardly through a work string that has been run into the inner diameter of the casing string and sealed off at its lower end. Because the work string by definition has a smaller inner diameter, fluid velocities in a work string configuration may be higher and may more efficiently transport the cuttings washed out of the annulus during cementing operations.
The reverse circulation cementing process, as opposed to the conventional method, may provide a number of advantages. For example, cementing pressures may be much lower than those experienced with conventional methods. Cement composition introduced in the annulus falls down the annulus so as to produce little or no pressure on the formation. Fluids in the wellbore ahead of the cement composition may be bled off through the casing at surface. When the reverse-circulating method is used, less fluid may be handled at surface and cement retarders may be utilized more efficiently or eliminated altogether.
In many applications, float devices are used as the casing is run into the wellbore. Float shoes and float collars typically contain a back pressure check valve to prevent the flow of fluid into the bottom of the casing string as the casing is run into the wellbore or once the casing has reached its target depth. Float apparatuses may be used to prevent back flow of cement composition into the casing inner diameter after the cementing operations have been completed. Float apparatuses may also prevent oil and/or gas under high pressure from entering the inner diameter of the casing as the casing string is being run into the wellbore. If gas or oil under high pressure does enter the wellbore, it can result in a well blowout. Additionally, the weight of the casing, particularly with deep wells, often creates a tremendous amount of stress and strain on the derrick surface equipment and on the casing. Float apparatuses may minimize that stress as the casing is lowered into the wellbore because they make the casing string more buoyant in the wellbore.